Known methods of synthesizing proteins include methods performed in living cells and methods performed in cell-free protein synthesis systems. A protein synthesized in any of those synthesis systems (hereinafter, also referred to as a “recombinant protein”) can be utilized after purification with an appropriate method. Various methods for protein purification have been used depending on the types of proteins to be purified. Out of those methods, methods in which a protein to be synthesized is synthesized as a fusion protein having a peptide called “tag” using the synthesis system as described above and the purification of such a protein is then carried out by using an affinity support on which a substance that specifically binds to the tag peptide have been effectively used.
As a usage of a recombinant protein, for example, in the case of using it for the structural analysis and the like, an extremely high degree of purity of such a protein is required (see “Basic Experimental Techniques for Proteins and Enzymes”, Nankodo Co., Ltd., 1981). In addition, when a recombinant protein is used in a functional analysis, one having a higher degree of purity is required. However, a target protein is rarely purified to a high degree even though the method of purifying a protein by using an affinity support as described above is performed, so that a combination of a plurality of purification has been required.
Such protein purification with a combination of plural kinds of purification methods is not only complicated in operation but also causes an increase in loss of a target protein in each purification step. Thus, there are problems in such a case as structural analysis where a large amount of protein is required.
Therefore, in order to solve those problems, a purification method having high purification efficiency has been desired.
Meanwhile, methods of performing interaction analysis between a protein and a substance have been used in general. However, if a target protein solution to be used in any of those methods contains substances which do not normally interact but bind nonspecifically, there are problems that a lot of pseudo-positive results are obtained and analytical efficiencies are very low in the case where a support or the like, which carries a substance with which the protein interacts, is allowed to contact with the protein to obtain the protein which binds to the substance. Therefore, a method of analyzing the interaction between a protein and a substance with high efficiency, which will solve those problems, has been desired.